Đk : x khác 0 

=> 35/2x + 720/x = 1/2

=> 35+1440/2x = 1/2

=> 1475/2x = 1/2

=> 1475 = 1/2 . 2x = x

Vậy x = 1475

k mk nha

X=1475

70:4x + 720/x = 1/2

=> 70/4x + 2880/4x = 1/2

=> 2950/4x = 1/2

=> x = 1475

Ta co:4x+720/x=70/1/2

4x+720/x=140

Gặp cả 2 vế lên x lan,ta co

4x+720=140x

720=136x(bớt cả 2 vế đi 4x)

x=720/136=

\(70:4x+\frac{720}{x}=\frac{1}{2}\)

\(\Leftrightarrow\frac{35}{2x}+\frac{1440}{2x}=\frac{x}{2x}\)

\(\Leftrightarrow35+1440=x\)

\(\Leftrightarrow x=1475\)

ý của mk k ph như z =((((

\(\left(x+\frac{2}{3}\right)\left(\frac{5}{4}-2x\right)>0\)

th1 : 

\(\hept{\begin{cases}x+\frac{2}{3}>0\\\frac{5}{4}-2x>0\end{cases}\Rightarrow\hept{\begin{cases}x>-\frac{2}{3}\\-2x>-\frac{5}{4}\end{cases}\Rightarrow}\hept{\begin{cases}x>-\frac{2}{3}\\x>\frac{5}{8}\end{cases}\Rightarrow}x>\frac{5}{8}}\)

th2 : 

\(\hept{\begin{cases}x+\frac{2}{3}< 0\\\frac{5}{4}-2x< 0\end{cases}\Rightarrow\hept{\begin{cases}x< -\frac{2}{3}\\-2x< -\frac{5}{4}\end{cases}\Rightarrow}\hept{\begin{cases}x< -\frac{2}{3}\\x< \frac{5}{8}\end{cases}\Rightarrow}x< -\frac{2}{3}}\)

vậy_

\(70:\frac{4x+720}{x}=\frac{1}{2}\)

\(\frac{4x+720}{x}=70:\frac{1}{2}\)

\(\frac{4x+720}{x}=140\)

\(4x+720=140x\)

\(4x-140x=-720\)

\(-136x=-720\)

\(x=\frac{-720}{-136}\)

\(x=\frac{90}{17}\)

\(\frac{70x}{4x+720}=\frac{1}{2}\)

\(140x=4x+720\)

\(136x=720\)

        \(x=720:136\)

        \(x=\frac{90}{17}\)

\(70\div\frac{4x+720}{x}=\frac{1}{2}\)

=> \(70\cdot\frac{x}{4x+720}=\frac{1}{2}\)

=> \(\frac{70x}{4x+720}=\frac{1}{2}\)

=> \(70x\cdot2=4x+720\)

=> \(140x=4x+720\)

=> \(140x-4x=720\)

=> \(136x=720\)

=> \(x=\frac{720}{136}=\frac{90}{17}\)